False walled pressure vessel

ABSTRACT

A generally cylindrical pressure vessel for use in treating an article with a fluid under high pressure characterized in that one or more flat metal plates are arranged within the vessel so as to define an article treating chamber and one or more balancing compartments arranged intermediate the treating chamber and the cylindrical side wall and/or double curved end wall or walls of the vessel. The plates are capable of sustaining treating chamber loadings not substantially in excess of the hydrostatic head of the treating fluid; and a balancing fluid, which is introduced into the compartments is employed to balance high treating chamber loadings substantially in excess of the hydrostatic head. A control is employed to sense and compare pressures in the treating chamber and compartments and to terminate the introduction of fluid producing the high treating chamber loadings when such pressures are out of balance.

United States Patent 1 Piegza Dec. 4, 1973 FALSE WALLED PRESSURE VESSEL [75] Inventor: Henry J. Piegza, Clarence, N.Y.

[73] Assignee: WSF Industries, Inc., Tonawanda,

22 Filed: Dec. 16,1971

21 Appl. No.: 208,554

UNITED STATES PATENTS 3,282,459 11/1966 Wilson 220/10 X 3,049,835 8/1962 Sundstrum..... 220/10 X 2,470,776 5/ 1949 Jewell 220/ l 0 Primary ExaminerAlan Cohan Attorney-John B. Bean et al.

[5 7 ABSTRACT A generally cylindrical pressure vessel for use in treating an article with a fluid under high pressure characterized in that one or more flat metal plates are arranged within the vessel so as to define an article treating chamber and one or more balancing compartments arranged intermediate the treating chamber and the cylindrical side wall and/or double curved end wall or walls of the vessel. The plates are capable of sustaining treating chamber loadings not substantially in excess of the hydrostatic head of the treating fluid; and a balancing fluid, which is introduced into the compartments is employed to balance high treating chamber loadings substantially in excess of the hydrostatic head. A control is employed to sense and compare pressures in the treating chamber and compartments and to terminate the introduction of fluid producing the high treating chamber loadings when such pressures are out of balance.

14 Claims, 7 Drawing Figures PATFNTED E 4 9 5 SHEET 1 BF INVENTORQ HENRY .J. P/EGZA (3W PQM A TTOPNEYS PATENTEDUEE 41975 11776257 SHEET 2 BF 3 JINVENTOR. HEN/PYJ. P/EGZA A TT ORNEYS PATENTEIJHEC 4 I975 3776257 SHEET 30? 3 FALSE WALLED PRESSURE VESSEL BACKGROUND OF THE INVENTION Pressure vessels of the type having a cylindrical side wall and either convex or concave end walls are commonly employed to enclose an article or materials being subject to a high pressure treating operation, such as for instance an impregnating operation. In that an article being treated normally does not substantially fill the pressure vessel because of its shape or size, there exists unused areas within the vessel, which nevertheless must be filled with impregnating material in order to insure that the article being treated is fully immersed. Clearly, the need to employ quantities of impregnant not actually used in the impregnating opera tion is at all times an economic disadvantage.

With the above problem in mind, it has become common practice when treating articles in reel form, to provide a plug or core concentrically positioned within a vessel or tank for receipt within the hub of the reel, as evidenced by US. Pat. No. 3,125,466.

However, attempts to provide treating chambers of non-circular cross section and/or with flat end walls within cylindrical vessels have met with only limited success. In this respect, the present practice of filling unused bounding areas of a pressure vessel with con crete or other filling material normally presents serious expansion problems and greatly adds to both the cost and weight of the vessel.

SUMMARY OF THE INVENTION The present invention relates to high pressure vessels of the type commonly used in the treating of an article with a fluid under pressure, and more particularly to improvements in such vessels, which minimize the volume of treating fluid required to be employed therewithin.

In accordance with the present invention, thin, flat metal plates are weld affixed to the cylindrical side wall and/or double curved end wall of a conventional pressure vessel, so as to define an article treating chamber bounded by one or more unusable space occupying outer balancing compartments. The number of plates and their arrangement within the pressure vessel will be dictated by the normal size and/or shape of the article or articles to be treated. Thus, where the article to be treated is in the form of a reel, metal end plates would be employed to block off the unusable space adjacent ends of the pressure vessel. Where the article to be treated is of a generally rectangular cross-sectional configuration, such as for instance pallet carried articles, four side plates would be affixed to the cylindrical side wall of the pressure vessel in order to define a treating chamber of corresponding rectangular crosssectional configuraton and, if desired, one or more end plates may be employed, as indicated above.

It is a particular feature of the present invention that inexpensive or easy to handle fluid, as compared to the impregnant or impregnant pressurizing fluid, is introduced into the balancing compartments at a pressure corresponding to the greater than atmospheric pressure applied to the impregnant within the treating chamber. By this arrangement, the bounding plates need only have a strength sufficient to withstand the hydrostatic pressure of the impregnant and thus may be inexpensively formed and installed. To insure against rupture of the bounding plates, the pressure of the balancing fluid within. the balancing compartments is continuously compared with the pressure within the treating chamber by a suitable control adapted to bleed off or terminate the introduction of pressurizing and balancing fluids whenever an undesirable disparity exists therebetween.

Depending upon the installation, the balancing fluid may be either a gas, such as air or nitrogen, or aliquid, such as water.

DRAWINGS The nature and mode of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of a horizontally disposed pressure vessel employing the present invention;

FIG. 2 is a sectional view taken generally along line 2-2 in FIG. 1;

FIG. 3 is a fragmentary vertically sectional view of the horizontally disposed pressure vessel employing a modified form of the present invention;

FIG. 4 is a vertical sectional view of an upstanding pressure vessel incorporating a further modification of the present invention;

FIG. 5 is a view similar to FIG. 4, but showing a further modification of the present invention;

FIG. 6 is a schematic view illustrating a pressure responsive control for use in the practice of the present invention.

FIG. 7 is a view similar to FIG. 1, but showing an altemative form of the present invention.

DETAILED DESCRIPTION The present invention possesses utility in combination with vessels of the type employed in performing diverse high pressure fluid, article treating operations, such as by way of example the oil impregnation of metal castings and the cooking of meat products. Normally, in performing these operations an article or group of articles to be treated are placed within a treating chamber, wherein the chamber is first placed under vacuum in order to remove included gases from the article and is subsequently filled with a treating fluid to a depth sufficient to immerse the article; the treating fluid being maintained under a high pressure to insure that the article is thoroughly impregnated with such fluid. When the treating fluid is a liquid, a compatible gas is normally applied to the surface of the liquid in order to establish the desired high pressure condition, whereas when the treating fluid is in a gaseous form, the treating gas is normally introduced into the treating chamber at the desired pressure.

As by way of more specific illustration, reference is made particularly to FIGS. 1 and2 wherein the present invention is shown as being incorporated within a conventional, horizontally disposed high pressure vessel 10 of the type employed to impregnate an article or group of articles with a liquid. Vessel 10 is shown as including a metal shell 12 having a cylindrical side wall 14 and a convex end wall 16; a metal door 18 for closingan access opening to a treating chamber20, such opening being defined for example by an open end 22 of the shell; a conduit 24 for admitting treating liquid to and withdrawing it from chamber 20; and :a conduit 26for placing chamber 20 in communication with a source of vacuum and for admitting a gas under pressure to and withdrawing it from chamber 20. As will be apparent, the illustrated cylindrical configuration of side wall 12 and double curved configured end wall 16 and door 18 are conventionally employed to permit the vessel to withstand high internal pressures determined by the pressure of pressurizing gas admitted through conduit 26. Of course, the gas admitted via conduit 26 will be compatible with the treating liquid.

Normally, suitable means, such as beams 28 are employed to support an article or an article carrier, such as a pallet within the treating chamber. Also, it is conventional to arrange a suitable level guage 30 within chamber 20 in order to control operation of liquid flow control valve 32 via a suitable electric and/or pneumatic admission-exhaust control 34, and to arrange a suitable pressure sensor 36 within chamber 20 for the purpose of controlling operation of gas flow control valve 38 via a suitable electric and/or pneumatic admission-exhaust control 39. Thus, in operation of a conventional system, after a vacuum is drawn to remove included gases from an article within chamber 20, as by applying a vacuum to conduit 26, an impregnating fluid is introduced into the chamber to a height sufficient to immerse the article, as determined by level gauge or sensor 30, and finally a compatible gas is introduced over the impregnating liquid to maintain a desired treating pressure thereon, as determined by sensor 36. conventionally, pre-set timing devices control operation of controls 34 and 39 to provide for automatic operation of the vessel.

As will be apparent, when the article to be treated, either because-of its shape or size does not completely fill chamber 20, there will exist unused side and end areas of chamber 20, which nevertheless must be filled with an ofttimes expensive impregnating liquid. In other words, the walls of vessel are necessarily curved to withstand high article treating pressure conditions and therefore define a vessel chamber, which has a configuration normally differing from some given configuration (including size) of an article to be treated, such that at least a portion of the vessel chamber 20 adjacent its curved wallsis unoccupied by the article. This unoccupied portion is unusable space, which .in a conventional vessel construction must be filled by the article treating fluid.

Thus, in accordance with the present invention, the vessel illustrated in FIGS. 1 and 2 is modified by blocking off unoccupied areas of chamber 20, which would not be required, as for instance in the case of articles removably positioned in the chamber on a rectangular pallet. To this end, vessel 12 is modified for instance by affixing a bottom plate 40 and a pair of side plates 41, 42 to vessel side wall 14 and end wall 16 as indicated in FIG. 1 to provide three fluid sealed arcuate bounding compartments or chambers 40a-42a, and by affixing a single metal plate 44 to end wall 16 and side and bottom plates 40, 41 and 42 to provide a flat closed end for chamber 20 and an end bounding compartment or chamber 44a; compartments 40a-42a being end sealed relative to vessel open end 22 by transverse flanges 46. Since the manner in which plates 40, 41, 42 and 44 are mounted within vessel 10 and connected to each other is a mere matter of choice or determined by the configuration of the article to be treated, it will be understood that end plate 44 may alternately extend completely across inside of the vessel and the rear ends of plates 40, 41 and 42 joined thereto.

The thus defined compartments are placed in communication with conduit 26 via branch conduits 48 for the purpose of continuously establishing therewith pressure conditions corresponding to the vacuum and gas pressure conditions existing within chamber 20. The actual pressures existing within compartments 40a, 41a, 42a and 44a are continuously monitored by suitable pressure sensors 40b, 41b, 42b and 44b and the output of such sensors continuously applied to control 39, wherein they are compared with the output of treating chamber pressure sensor 36. If one or more of the pressures sensed in the compartments is different than that existing in chamber 20 by a predetermined amount because of line blockages or leaks, control 39 may automatically control valve 38 to terminate the vacuum treating or pressurizing operation and, if desired, over control 34 for the purpose of exhausting impregnating treating fluid through valve 32.

Devices for comparing the outputs of plural pressure sensors and controlling the operation of flow control valves in accordance with differences in sensed pressures are per se well known, and thus a detailed description is believed unnecessary. However, to facilitate understanding of present invention, reference may be made to FIG. 6, wherein control 39 is shown as being pneumatically operated and as including a plurality of diaphragm operated electrical switches (only 39a and 39d being shown), which close whenever the pressure in chamber line 36 from sensor 36 is more or less than the pressures in the compartment lines from sensors 40b-42 b and 44b (only compartment lines 40b and 44b being shown) by a predetermined amount. Upon closing of any of the diaphragm switches, a circuit is established through a suitable control device or relay 39, which in turn controls valve 38 and, if desired, control 34. Of course, control 39 would preferably be of a type capable of functioning under both pressure and vacuum conditions.

As will be apparent, by maintaining the pressures existing in compartments 40a, 41a, 42a and 44a essentially equal, plates 40, 41, 42 and 44 need only be of sufficient thickness or strength to withstand with a slight margin of safety the hydrostatic pressure imposed thereon by the treating liquid. As a result, the plates forming common boundaries between the treating chamber occupied by the article and balancing compartments may be formed of relatively light weight, inexpensive, thin, flat metal stock and may be economically fixed to the vessel wall surfaces as by welding.

If the pressurizing gas is relatively expensive, due for instance to the requirement that such gas must be nonreactive with the treating liquid, the boundary compartments may be isolated relative to the pressurizing gas present in the treating chamber and connected to a separate source of relatively inexpensive fluid under pressure, such as air or water. This may be effected by modifying the construction of FIG. 1, as indicated in FIG. 7, by separately supplying the chamber with a non-reactive pressurized gas via a valve controlled conduit shown as 26a. Thus, the conduit arrangement and associated control would be essentially identical to that hereinafter described with reference to FIG. 3, except that conduit 24 would be retained for the purpose of admitting treating liquid to and withdrawing such liquid from the chamber. In this case, care'should be taken in the design of the vessel to account for both the hydrostatic pressure of the treating liquid and the boundary liquid.

The construction illustrated in FIGS. 1 and 2 may be further modified by deleting end plate 44 or all of side bottom plates 40-42 as required to accommodate the vessel to receive articles of diverse sizes and/or shapes. If the side plates are omitted, the end plate may be peripherally affixed to end wall 16 onto the side wall 14 immediately adjacent end wall 16.

FIG. 3 illustrates a modified form of the present invention, having utility where the treating fluid supplied via conduit 26 is a relatively expensive gas and the balancing fluid is a relatively inexpensive fluid, such as air supplied through a separate conduit 26' under the control of valve 38'. In that the treating fluid is a gas, which occupies the whole of the treating chamber when under pressure, it is preferable to additionally provide a top plate 50 to define a top boundary compartment 500. Of course, compartmentSOa would be placed in communication with conduit 26 and be provided with a pressure sensor 50b. Since the hydrostatic head" of the treating gas is exceedingly small, the boundary plates need only be of sufficient thickness to prevent puncture thereof in the event of careless handling of articles within the vessel. If the balancing fluid is a liquid such as water, the hydrostatic head of the balancing fluid must be considered in designing the boundary plates.

FIG. 4 illustrates the utilization of the present invention in combination within a pressure vessel having a top opening upstanding vessel 52 into whieh a treating liquid is admitted via a conduit 54 to a level determined by sensor 56. In this form of the invention, four vertically rising metal plates 58 have their vertical marginal edges fixed to cylindrical side wall 60 of vessel 52 and their bottom marginal edges fixed to bottom end wall 62, thereby to define asquare cross-sectional treating chamber 64 bounded by four arcuate boundary compartments 66. In that sensor 56 serves to maintain the treating fluid within treating chamber 64 at a level below the upper edges of plates 58, chamber 64 may remain in fluid communication with compartments 66 adjacent the upper end of the vessel. This greatly simplifies the construction, since acompatible pressuring gas may be simultaneously supplied to the treating chamber and compartments by a single conduit 70 under the control of a single pressure sensor 72.

Reference is now made to FIG. 5, which illustrates a further modification of the invention particularly adapted for use in vessels employed in processing cylindrical articles. In this construction, treating fluid such as an expensive gas is admitted to and withdrawn from the cylindrical treating chamber 80 of an upstanding vessel 82 by conduit 84 under control of chamber pressure sensor 86, control 90 and valve 92. The unusable top and bottom regions of the vessel adjacent vessel door 94 and bottom end wall 96 are blocked off from chamber 80 by upper and lower end plates 98 and 100 to define upper and lower boundary compartments 98a and 100a, respectively. A relatively inexpensive fluid, such as air, is supplied to compartments 98a and 1000 through a branched conduit 102 under the control of valve 104, which is in turn controlled by boundary compartment pressure sensors 98b and l00b and control 90. Control 90, which may be of a construction similar to that of control 39, serves to compare the pressures sensed by sensors 86, 98b and Gb for the purpose of controlling valves 92 and 104, if a predetermined disparity exists between the pressures in chamber and compartments 98a and a.

I claim:

I A high pressure vessel for treating an article therewithin, which comprises in combination:

a metal shell including a generally cylindrical side wall having an access opening closeable by a metal door and at least one end wall of double curvature configuration thereby to permit said shell to withstand at least a high predetermined article treating internal pressure;

a metal plate affixed to an inner surface of said shell whereby to define a fluid sealed boundary between an article treating chamber accessible through said access opening and a balancing compartment arranged intermediate said plate and said inner sur face;

means for admitting an article treating fluid into said treating chamber and maintaining said treating fluid under said predetermined treating pressure; and

means for supplying a balancing fluid differing from said treating fluid to said balancing compartment at a pressure substantially equal to said predetermined pressure, said plate being characterized as being substantially flat and of a construction able to withstand without failure a pressure in excess of that corresponding to the hydrostatic head of either said treating fluid or said balancing fluid but substantially less than said predetermined pressure.

2. A pressure vessel according to claim 1, wherein said shell vertically upstands, said plate is weld affixed to said inner surface of said shell whereby to define a vertically extending boundary between said treating chamber and said balancing compartment, said treating fluid is a liquid, said means for supplying said treating fluid includes means for maintaining the level of said treating liquid below an upper end of said plate, said means for supplying a balancing fluid supplies a gas under said predetermined pressure to said balancing compartment, and said means for maintaining said treating fluid under said predetermined pressure places said treating chamber and said balancing compartment in free flow communication adjacent said upper end of said plate above said level of said. treating fluid.

3. A pressure vessel according to claim 1, wherein said treating fluid is a gas supplied to said treating chamber under said predetermined pressure.

4. A pressure vessel according to claim 1, wherein said treating fluid is a liquid and said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber.

5. A pressure vessel according to claim 4, wherein said pressurizing fluid and said balancing fluid are gas and supplied from a common source.

6. A pressure vessel according to claim 4, wherein said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid,"and said balancing fluid is air.

7. A pressure vessel according to claim 4, wherein said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid, and said balancing fluid is liquid.

8. A pressure vessel according to claim 1, wherein said plate is peripherally weld aflixed to said inner surface of said shell immediately adjacent the junction of said side and said end wall, thereby said balancing compartment is arranged intermediate said plate and said end wall.

9. A pressure vessel according to claim 1, wherein said means for supplying said balancing fluid includes means for comparing pressures in said chamber and said compartment and for controlling said means for maintaining said treating fluid under said predetermined treating pressure and said means for supplying balancing fluid whereby to prevent differences in pressure between said chamber and compartment from exceeding an amount producing failure of said plate.

10. A pressure vessel according to claim 9, wherein said treating fluid is a liquid, said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber, said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid, and said balancing fluid is air.

11. A pressure vessel according to claim 9, wherein said treating fluid is a liquid, said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber, and said pressurizing fluid and said balancing fluid are gas and supplied from a common source.

12. A pressure vessel according to claim 1, wherein said access opening is in a wall of said shell remote from said one end wall, said plate is weld affixed to said inner surface of said shell to define said balancing compartment extending lengthwise of said shell intermediate said plate and said cylindrical side wall.

13. In a high pressure vessel for treating an article of a given configuration therewithin, said vessel having walls curved to withstand at least a high predetermined article treating pressure condition and a closeable access opening for removably positioning said article within said vessel, said walls defining a chamber characterized as having a configuration differing from said given configuration whereby when said article is placed within said chamber at least one portion of said chamber adjacent said curved walls is unoccupied by said article and thus creates unusable space, and means for admitting an article treating fluid into said chamber and maintaining said treating fluid under said predetermined treating pressure, the improvement for reducing the quantity of treating fluid required to be admitted by an amount corresponding essentially to said one portion of said chamber which comprises in combination: means fixed to said curved walls for forming a fluid sealed boundary between said one portion and that portion of said chamber occupied by said article whereby to divide said chamber into an article treating chamber to be occupied by said article and a balancing compartment comprising said one portion, said treating chamber being in communication with said access opening and said means for admitting treating fluid; and means for supplying a balancing fluid differing from said treating fluid to said balancing'compartment at a pressure substantially equal to said predetermined pressure, and said means fixed to said curved walls including a flat metal plate forming a common boundary of said treating chamber and said boundary compartment, said plate being characterized as being of a construction able to withstand without failure a pressure in excess of that corresponding to the hydrostatic head of either said treating fluid or said balancing fluid but substantially less than said predetermined pressure. 14. The improvement according to claim 13, wherein means are provided for sensing pressures in said treating chamber and said boundary compartment, for comparing pressures sensed in said treating chamber and said boundary compartment, and for controlling operation of said treating fluid admitting and pressure maintaining means and said balancing fluid supply means whereby to prevent differences in pressure in said treating chamber and compartment from exceeding an amount producing failure of said plate. 

1. A high pressure vessel for treating an article therewithin, which comprises in combination: a metal shell including a generally cylindrical side wall having an access opening closeable by a metal door and at least one end wall of double curvature configuration thereby to permit said shell to withstand at least a high predetermined article treating internal pressure; a metal plate affixed to an inner surface of said shell whereby to define a fluid sealed boundary between an article treating chamber accessible through said access opening and a balancing compartment arranged intermediate said plate and said inner surface; means for admitting an article treating fluid into said treating chamber and maintaining said treating fluid under said predetermined treating pressure; and means for supplying a balancing fluid differing from said treating fluid to said balancing compartment at a pressure substantially equal to said predetermined pressure, said plate being characterized as being substantially flat and of a construction able to withstand without failure a pressure in excess of that corresponding to the hydrostatic head of either saId treating fluid or said balancing fluid but substantially less than said predetermined pressure.
 2. A pressure vessel according to claim 1, wherein said shell vertically upstands, said plate is weld affixed to said inner surface of said shell whereby to define a vertically extending boundary between said treating chamber and said balancing compartment, said treating fluid is a liquid, said means for supplying said treating fluid includes means for maintaining the level of said treating liquid below an upper end of said plate, said means for supplying a balancing fluid supplies a gas under said predetermined pressure to said balancing compartment, and said means for maintaining said treating fluid under said predetermined pressure places said treating chamber and said balancing compartment in free flow communication adjacent said upper end of said plate above said level of said treating fluid.
 3. A pressure vessel according to claim 1, wherein said treating fluid is a gas supplied to said treating chamber under said predetermined pressure.
 4. A pressure vessel according to claim 1, wherein said treating fluid is a liquid and said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber.
 5. A pressure vessel according to claim 4, wherein said pressurizing fluid and said balancing fluid are gas and supplied from a common source.
 6. A pressure vessel according to claim 4, wherein said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid, and said balancing fluid is air.
 7. A pressure vessel according to claim 4, wherein said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid, and said balancing fluid is liquid.
 8. A pressure vessel according to claim 1, wherein said plate is peripherally weld affixed to said inner surface of said shell immediately adjacent the junction of said side and said end wall, thereby said balancing compartment is arranged intermediate said plate and said end wall.
 9. A pressure vessel according to claim 1, wherein said means for supplying said balancing fluid includes means for comparing pressures in said chamber and said compartment and for controlling said means for maintaining said treating fluid under said predetermined treating pressure and said means for supplying balancing fluid whereby to prevent differences in pressure between said chamber and compartment from exceeding an amount producing failure of said plate.
 10. A pressure vessel according to claim 9, wherein said treating fluid is a liquid, said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber, said pressurizing fluid is a gas characterized as being non-reactive with said treating liquid, and said balancing fluid is air.
 11. A pressure vessel according to claim 9, wherein said treating fluid is a liquid, said means for admitting and maintaining said treating fluid under said predetermined pressure includes means to supply a pressurizing fluid to said treating chamber, and said pressurizing fluid and said balancing fluid are gas and supplied from a common source.
 12. A pressure vessel according to claim 1, wherein said access opening is in a wall of said shell remote from said one end wall, said plate is weld affixed to said inner surface of said shell to define said balancing compartment extending lengthwise of said shell intermediate said plate and said cylindrical side wall.
 13. In a high pressure vessel for treating an article of a given configuration therewithin, said vessel having walls curved to withstand at least a high predetermined article treating pressure condition and a closeable access opening for removably positioning said article within said vessel, said walls defining a chamber characterized as having a configuration differing from said given configuration wHereby when said article is placed within said chamber at least one portion of said chamber adjacent said curved walls is unoccupied by said article and thus creates unusable space, and means for admitting an article treating fluid into said chamber and maintaining said treating fluid under said predetermined treating pressure, the improvement for reducing the quantity of treating fluid required to be admitted by an amount corresponding essentially to said one portion of said chamber which comprises in combination: means fixed to said curved walls for forming a fluid sealed boundary between said one portion and that portion of said chamber occupied by said article whereby to divide said chamber into an article treating chamber to be occupied by said article and a balancing compartment comprising said one portion, said treating chamber being in communication with said access opening and said means for admitting treating fluid; and means for supplying a balancing fluid differing from said treating fluid to said balancing compartment at a pressure substantially equal to said predetermined pressure, and said means fixed to said curved walls including a flat metal plate forming a common boundary of said treating chamber and said boundary compartment, said plate being characterized as being of a construction able to withstand without failure a pressure in excess of that corresponding to the hydrostatic head of either said treating fluid or said balancing fluid but substantially less than said predetermined pressure.
 14. The improvement according to claim 13, wherein means are provided for sensing pressures in said treating chamber and said boundary compartment, for comparing pressures sensed in said treating chamber and said boundary compartment, and for controlling operation of said treating fluid admitting and pressure maintaining means and said balancing fluid supply means whereby to prevent differences in pressure in said treating chamber and compartment from exceeding an amount producing failure of said plate. 